In barrel pumps of this nature (DE-PS No. 34 12 873), two problems arise, especially if environmentally harmful liquids are involved. One problem consists in that moving the pump from one barrel into another with the motor running is not possible, because the liquid runs out of the pump at its lower open end. Such change is necessary if very rapid emptying of several barrels is required. The second problem consists in that the barrels cannot be emptied completely and, due to the inlet openings being arranged at a distance from its lower end, an amount of residual liquid corresponding to the distance of the openings to the end of the housing wall remains in the barrel. To this residual quantity is added the amount of liquid still present in the pump, which upon turning off the motor runs back into the barrel. The thus remaining residual quantity impairs recycling of the barrels.
It is the goal of the invention to reduce the residual quantity remaining in the barrel to a minimum amount.